The present invention relates to plasma processing modules for the processing of a semiconductor substrate in the manufacture of integrated circuits. More particularly, the present invention relates to downstream, inductively coupled plasma processing modules and methods of using the modules during the processing of the semiconductor substrates.
Semiconductor substrates are typically processed using plasma processing modules to perform various process steps during the manufacture of the semiconductor devices. Generally, these plasma-enhanced processes are well known to those skilled in the art and include various etching processes and stripping processes.
In recent trends, plasma-enhanced processes have been more frequently used to perform resist stripping. Traditionally, the resist stripping or ashing process has been considered a fairly straight forward process. However, due to the small feature size and increased complexity of devices now common in the semiconductor industry, conventional plasma processing modules tend to cause plasma-induced damage to the semiconductor devices during the processing of the semiconductor substrates. To more thoroughly illustrate the problems associated with the use of conventional plasma processing modules, a prior art inductively coupled plasma processing module 100 will be described with reference to FIG. 1.
As illustrated in FIG. 1, plasma processing module 100 includes a plasma chamber 102 formed by chamber walls 104 and dielectric window 106. Plasma processing module 100 includes a feed gas inlet 108 for allowing feed gasses 109 to flow into chamber 102. An exhaust port 110 is also provided for exhausting gases from chamber 102. An inductive source 112, typically taking the form of a coil positioned on dielectric window 106, is used to energize feed gases 109 within chamber 102 and strike a plasma within the chamber. In this example, inductive source 112 is powered by RF power supply 114.
With the above described configuration, the shape of inductive source 112 causes the plasma within chamber 102 to form a plasma having a primary dissociation zone 116. This primary dissociation zone is the region within the chamber that the plasma most efficiently dissociates feed gases 109 (for example O.sub.2 and H.sub.2 O vapor) into neutral non-charged species (for example O, H, and OH). In the case in which inductive source 112 takes the form of a coil attached to dielectric window 106, primary dissociation zone 116 takes the form of a generally donut shaped region located within chamber 102 directly below the coils of inductive source 112.
Still referring to FIG. 1, plasma processing module 100 also includes a liner 118, such as a quartz liner, for protecting the walls of the plasma chamber from the plasma and reducing the recombination of neutral radicals like O or OH. A chuck 120 is positioned in the bottom of chamber 102 and is configured to support a semiconductor substrate 122. As is known in the art, chuck 120 may be heated to improve the efficiency of the process. Plasma processing module 100 also includes a quartz baffle 124 located above substrate 122. Baffle 124 includes a plurality of openings 126 formed through baffle 124 which cause any gases flowing through chamber 102 to be redistributed so that the gases flow more evenly over substrate 122 than would be the case if baffle 124 were not included in module 100.
Although baffle 124 partially shields substrate 122 from direct exposure to the plasma, portions of substrate 122 remain directly exposed to the plasma. This direct exposure to the substrate to the plasma may cause different types of the plasma-induced damage. For example, in semiconductor substrates having small feature sizes such as 0.25 .mu.m devices, charge damage can occur when electrically charged species from the plasma accumulate non-uniformly on device gates and interconnections. This charge accumulation can lead to large voltage potentials across individual gates or between devices that can cause gate degradation or loss of gate integrity. Device damage has been found to correlate with the charge species dose that the device is exposed to during the process. Therefore, exposing the device directly to charged species produced within the plasma at high concentration (e.g., &gt;10.sup.11 /cm.sup.3) for even a short duration of time (e.g., seconds) or moderate concentration (e.g., 10.sup.9 /cm.sup.3 to 10.sup.10 /cm.sup.3) for a longer duration (e.g., tens of seconds) can cause significant problems for this type of device. In another example, device damage has been attributed to direct UV radiation exposure from the plasma. In the conventional configuration of an inductively coupled plasma processing module, such as module 100 described above, portions of substrate 122 are directly exposed to UV radiation from the plasma.
Another problem associated with conventional inductively coupled plasma processing modules such as module 100 is that they often provide relatively poor dissociation of the feed gases. In some cases, much of the RF energy is input into ionization at the expense of dissociation of the feed gas. This poor dissociation decreases the efficiency of and therefore increases the time necessary for processing, further contributing to the above described problem of charge damage to devices on the substrate. This poor dissociation is at least in part due to the fact that the feed gases 109 are not forced to flow directly through the primary dissociation zones 116. As mentioned above, primary dissociation zones 116 are the regions within chamber 102 in which the plasma most efficiently dissociates the feed gases.
The present invention provides improved designs for inductively coupled plasma processing modules and methods of using the novel modules to process semiconductor substrates. These designs provide an isolated plasma containment chamber within the module. This isolated plasma containment chamber prevents the semiconductor substrate from being directly exposed to line-of-sight UV radiation produced by the plasma and substantially reduces the concentration of charged species that the semiconductor substrate is exposed to compared to prior art inductively coupled plasma processing modules. Also, the plasma processing modules of the present invention provide a module that improves the dissociation of the feed gases compared to prior art inductively coupled plasma processing modules. This is accomplished by specifically controlling the flow of gases through the module.